This application claims priority of pending German Patent Application Nos. 101 24 569.6, 101 24 571.8, 101 24 572.6 and 101 24 573.4 all filed on May 14, 2001.
The invention relates to a power-driven screw drive comprising a housing having a main housing within which a drive, a reduction gear coupled therewith and a spindle received therein are supported, further comprising an angle head having a tool spindle for driving a tool, the tool spindle driven by the spindle and arranged at an angle thereto, and further comprising an angle head housing that is connected adjustably with the main housing via an adjusting device.
Such a screw drive is known from EP 0 691 185 A1.
From WO 99/16858, a power screwdriver having a torque limiting coupling releasing torque-dependently is known comprising a first coupling part, a second coupling part, a spring element for axially biasing both coupling parts against each other, and further having at least one roll body rolling between both coupling parts, the at least one roll body coupling both coupling parts when driving the screwdriver up to a preset release moment, when tightening a screw.
Angle-type screwdrivers having an adjustable angle head within which a tool spindle for driving a tool is received at an angle to a spindle driven by a gear, have several advantages with respect to other power-driven screwdrivers the tool receptacle of which is received directly on the spindle and which are thus oriented in the longitudinal direction of the screwdriver. On the one hand, the possibility for adjusting the tool head allows different operating positions, allowing in many cases a more economic operation, even under confined conditions. On the other hand, the reaction moment received by the screwdriver during tightening and loosening of screws does not lead to a turning of the screwdriver about its longitudinal axis, but to a pivoting of the screwdriver about the angle head. Such pivot movements can be controlled by the operator much easier than a rotation of the screwdriver about its longitudinal axis.
The angle-type screwdriver known from EP 0 691 185 A1 mentioned at the outset, comprises a rotatable angle head which is connected to a main housing of the angle-type screwdriver by a screw connection. Within the main housing, a drive and a reduction gear of the angle-type screwdriver are supported fixedly against rotation. The screw connection is arranged directly at the transition from the angle head to the main housing and is secured by a securing nut against unintentional rotation. When operating the angle-type screwdriver between the angle head and the main housing part, relatively large torques may occur. Therefore, there is an additional retention against rotation by providing a locking pin. In a locking position, the locking pin extends through bores within which the angle head and the main housing extend in radial direction in the region of the screw connection. In this way, the angle head can be locked fixedly against rotation with respect to the main housing in several positions, so that the angle head cannot change its position unintentionally when operating the angle-type screwdriver.
It is a first object of the invention to provide an improved angle-type screwdriver allowing for a relative rotation between the angle head and the main housing a particularly simple and cost-effective way.
It is a second object of the invention to allow an easy adjustment of the angle head with respect to the housing even during operation of the angle-type screwdriver.
It is a third object of the invention to provide an angle-type screwdriver having a torque limiting coupling having high reliability and low wear during operation.
It is another object of the invention to provide a power screwdriver allowing for a precise adjusting for the tightening torque of a screw.
It is still a further object of the invention to provide a power screwdriver of high reliability having a torque limiting coupling with low wear in operation.
These and other objects are solved by the invention by the fact that the reduction gear comprises a reaction part receiving a reaction moment with respect to the spindle, the reaction part being connected with the angle head housing fixedly against rotation and being coupled to the drive adjustably.
The reduction gear may be any gear suitable for transmitting torque from an input end to an end and having a transmission ratio of less than one, which means that there will be a lower output than input speed. A reduction gear will transmit a higher torque at its output end than it receives at its input end. The reaction torque resulting therefrom is received by a part which is called reaction part and which must be somehow supported externally. If the reaction part would not be supported externally, than the reaction part would freely rotate, when the input end is driven. Thus the reduction gear would not transmit the desired torque at its output end.
The reduction gear could for instance be a spur gear received within a gear housing, the gear housing forming the reaction part. Or the reduction gear may be a planetary gear comprising a hollow wheel within which planetary wheels and at least one sun wheel are received. The hollow wheel would then form the reaction part. Also any other type of gear can be used.
According to the invention, the connection of the reaction part with the angle head housing in a way fixedly against rotation while also coupling to the drive via an adjustment means leads to the consequence that the reaction part is connected to the angle head housing fixedly against rotation even when the adjustment device is completely released and thus the angle head can be rotated with respect to the main housing. By contrast, in prior art angle-type screwdrivers, the reaction part is always directly connected with the drive or with a housing part fixed thereto, without any adjustment possibility. The different connection of the reaction part with the two parts of the angle-type screwdriver that are adjustable thereto has important implications with respect to the torques that act between the angle head housing and the main housing and which must be absorbed by the adjusting device in operation.
For illustration, it may be assumed that the spindle is blocked by a screw that has been fully tightened so that the torque exerted by the drive must be fully absorbed between the housing parts of the angle-type grinder. In this case, the torque exerted by the drive operates between the drive and the reduction gear, on the one hand by a spindle section lying therebetween, and on the other hand, as a counter torque, between the housing parts which are connected with the reaction part of the reduction gear and with the drive, respectively. This torque is reduced by the reducing factor of the reduction gear with respect to the torque that acts between the reduction gear and the angle head. Thereby, the adjustment device can be constructed much simpler and not as sturdy as the adjustment devices necessary in prior art designs which allow an adjustable connection between the reaction part of the reduction gear and the angle head housing.
Due to the small torque that must be absorbed by the adjustment device, it is even possible to adjust the angle head during operation of the angle-type screwdriver or when the screw is fully tightened or blocked.
Any locking nuts or additional locking mechanisms become superfluous in this way. By contrast, it is sufficient to design the adjustment device as a simple screw connection. Alternatively, or in addition thereto, it is of course possible, to provide a locking mechanism, for instance if pre-defined relative positions between the angle head and the main housing are desired. However, such a locking mechanism is not necessary in view of the torque to be transmitted. However, if such a locking mechanism is desired, the mechanism may be very simple and light, since it must not absorb any considerable torque.
Of course, corresponding considerations are valid also with respect to angle-type screwdrivers in which the reaction part of the reduction gear is not supported directly by the angle head housing, but in which a torque limiting coupling is arranged therebetween.
Therefore, according to an advantageous development of the invention, the angle-type screwdriver comprises a torque limiting coupling having a first and a second coupling part, which engage with each other when the torque limiting coupling is engaged, thereby connecting the first coupling part with the angle head housing fixedly against rotation and to the drive via the adjustment means, the second coupling part being connected with the reaction part of the reduction gear fixedly against rotation.
When compared with torque limiting couplings that are arranged directly between two sections of a drive train, this design offers the advantage that there is no relative rotation between both coupling parts when the torque limiting coupling is engaged. Thereby, the coupling parts and any roll bodies arranged therebetween are not subjected to any large centrifugal forces that would lead to an increased wear. Since for the releasing of the torque limiting coupling both coupling parts must be withdrawn from each other, possibly against the power of a compression spring, the first or the second coupling part may be arranged axially slidable within the housing. To allow a relative rotation between both coupling parts, also one of these parts must be arranged rotatably within the housing.
According to a further development of this embodiment, the first coupling part is arranged within the housing axially slidable, and the reaction part is arranged freely rotatable with respect to the housing.
In this way, the possibilities of axial sliding and of rotation are assigned to different coupling parts, whereby the fixation to the housing of the angle-type grinder is simplified.
Also it is preferred to provide a switch for switching off the angle-type grinder, the switch being actuable by the first coupling part.
In this way, it is prevented that the drive continues to exert power onto the coupling parts, when the torque limiting coupling was released. Thus a continued revolution of the roll bodies between both coupling parts is avoided.
Also it is preferred, when the reaction part is configured as a hollow wheel comprising several planetary wheels of a planetary gear.
According to an alternative embodiment of the invention, on both coupling parts catches are provided for locking both coupling parts directly when driving the screwdriver in a second direction of rotation (loosening direction).
Since both coupling parts are directly locked with each other when a screw is released, very high torques can be transmitted between both coupling parts, in particular without utilizing the roll bodies between the coupling parts. Since the roll bodies do not have to transmit the torque when releasing or unscrewing a screw, the roll bodies are subject to considerably less wear than usually occurred in prior art torque limiting couplings. Also any cams, teeth, protrusions or steps which are engaged by the roll bodies, when the torque limiting coupling is engaged, are subject to the same advantages. By the way, under the term xe2x80x9clockingxe2x80x9d, any positive engagement between the two coupling parts shall be understood. Preferably, a positive fit of the catches between the coupling parts is effected in a two-dimensional way, so that also larger torques can be transmitted between the two coupling parts without any deformation.
Thus by the direct locking of both coupling parts, explicitly no provision is made for a torque dependent disengagement of the torque limiting coupling, when a screw is released or untightened. However, the lack of such a possibility for disengagement can be tolerated under safety considerations. Anyway, if such a torque dependent disengagement should be desired when releasing or untightening screws, then, for instance, a second torque limiting coupling could be included in the drive train which releases only at a higher torque when operated in reverse direction.
According to an alternative embodiment of the invention, the torque limiting coupling is coupled with the spindle by a loose coupling.
Thereby, it is ensured that the preset release moment is obtained exactly. According to the invention, it was found that any unprecise disengagement in prior art designs is due to the effect of the torque limiting coupling. In particular, when the torque limiting coupling is released after tightening a screw, then the torque limiting coupling effects a torque acting in the counter direction (loosening direction), i.e. the screw, after having reached the release moment is loosened again to a small extent. Since the magnitude of the torque acting in the loosening direction is not known, the actual tightening moment that was effected on the screw cannot be predicted exactly in the prior art designs.
In these designs the torque acting in the loosening direction when the torque limiting coupling releases, results from the fact that the pressure spring acting between both coupling parts continues to exert pressure, even after both parts have moved apart when the torque limiting coupling releases. This pressure then also acts via the roll bodies onto the other coupling part. This torque acting on the other coupling part causes a loosening moment affected on the spindle, thus leading to a loosening of the screw to be tightened.
According to the invention, a loose coupling between the torque limiting coupling and the spindle avoids that such a loosening moment might be transferred from the torque limiting coupling onto the spindle, since the loose coupling releases on its own when the direction of rotation is reversed.
The considerations explained before also hold true with respect to torque limiting couplings of different designs, for instance also with respect to torque limiting couplings integrated in a drive train and acting onto the spindle without any gear. Since torque limiting couplings for screwdrivers always include two coupling parts biased against each other, when the torque limiting coupling engages again after a release operation, a relative movement between the two coupling parts is always effected, thus leading to a loosening moment acting onto the spindle. Consequently, the concept of the loose coupling can also be applied advantageously to any other kind of power screwdriver, e.g. to a screwdriver of straight configuration, to avoid any loosening reverse moment when the torque limiting coupling releases.
According to a further embodiment of the invention, the roll bodies are configured as rolls.
Thereby, any point contact that usually occurs in prior art designs when using balls as roll bodies, is substituted by a linear contact. Thus, the forces acting on the roll bodies are distributed onto larger surfaces, whereby any wear of the roll bodies itself as well as any wear of the respective guide faces, by which the roll bodies are guided, are decreased considerably. Thereby, the design life of the torque limiting coupling is increased considerably and also the precise complying with a preset release moment is ensured.
The rolls may, for instance, by guided in hollow cylindrical recesses which are formed on the face sides of one of the coupling parts.
However, preferably the rolls are received rotatably on shafts supported by the first coupling part.
Such a guidance of a roll provides for low friction and thereby low wear of the roll. The bearing provided on one shaft may for instance be designed as a needle bearing allowing for high loading while still being of a space-saving design and ensuring low friction.
According to a preferred development of this design, the axes of rotation of the rolls determined by the shafts are arranged at a distance from the longitudinal axis of the first coupling part.
Thus, the axis of rotation of the roll does not extend through the longitudinal axis or axis of rotation of the first coupling part, but extends at an angle thereto. Thus, the direction of rotation of the roll is not in tangential direction, but is fixed at an angle with respect to the tangent. Thus, in one of both possible directions of rotation, which is preferably the working direction for tightening of screws, the rolls move in a self-centering way. Thereby, the rolls do not displace to the outset while moving about themselves, and thus cannot work against any housing parts surrounding the roll.
According to a further development of this design, the rolls are supported in a floating manner on their shafts.
Thereby, the supporting of the rolls on the shafts is simplified and also saves space, since fixation parts become superfluous.
According to a further development of this design, the shortest distance between the axis of rotation of each roll and the longitudinal axis of the first coupling part is between 5% and 15%, preferably between 9% and 11% of the distance between the center of the roll and the longitudinal axis.
It has been found that with such a design particularly good self-centering properties can be reached.
According to still another embodiment of the invention, a cam guide way extending circumferentially is provided on one of the coupling parts and is formed by several guide sections, preferably by three guide sections, all being of equal design.
Thereby, the release character of the torque limiting coupling can be influenced by the particular design of the cam guide way in a simple way. Also it is preferred, when each guide section comprises a cam, the flanks of which forming a leading side and a trailing side for a roll, which both may have different slopes.
Needless to say, the features mentioned before and to be explained hereinafter, cannot be utilized in the given combination, but also in different combinations or on its own, without leaving the scope of the invention. Further advantages and features of the invention may be taken from the following description of a preferred embodiment of the invention with reference to the enclosed drawings.